2010-11: Eric Brassard played AA midget hockey near his hometown of St-Hubert, Quebec.
2011-12: Brassard attended the Harrington College sports school in suburban Montreal. In nine games with the school's junior team he had a 5.72 goals against and .830 save percentage.
2012-13: Brassard was invited to Gatineau's camp as a free agent and played 29 games for the Olympiques in his first QMJHL season. The 17-year-old was 9-8 in 28 regular season games with a 3.92 goals against and .861 save percentage. He played one period in one playoff game; stopping six of seven shots. Brassard was ranked 22nd amongst North American goaltenders in Central Scouting's final rankings but was not selected in the 2013 NHL Draft.
2013-14: Brassard attended the Tampa Bay Lightning's prospect camp before joining the QMJHL's Charlottetown Islanders, who had obtained him in an August trade with Gatineau. Splitting time with Mason McDonald after the 17-year-old was acquired in a mid-season trade with Acadie-Bathurst, Brassard's numbers were inflated playing on an Islanders team near the bottom of the league standings. In 32 regular season games he was 7-20-1 with one shutout and had a 3.56 goals against and .901 save percentage. Brassard, in his second year of draft eligibility, was ranked 23rd amongst North American goaltenders in Central Scouting's mid-term rankings prior to the 2014 NHL Draft.